1. Field of the Invention
The present invention relates to integrated devices and, more specifically, to methods for fabricating micro-electromechanical systems (MEMS) structures and/or devices.
2. Description of the Related Art
Fabrication of a MEMS device often involves forming structures in one or more relatively thick (e.g., about 10 μm or thicker) layers of (poly)silicon. A typical prior-art method of forming such structures usually includes a sequence of: (1) patterning and etching a thick (poly)silicon layer down to an underlying silicon-oxide, etch-stop layer, which etching produces variously sized voids (some relatively deep and narrow) in the (poly)silicon layer; (2) filling the voids with silicon oxide; and (3) planarizing the surface of the silicon oxide in preparation for the deposition and processing of the subsequent over-layers required to complete the fabrication process of the MEMS device. One significant difficulty associated with the oxide-filling step (i.e., step (2)) is that it often requires multiple deposition, etch-back, annealing, and polishing steps to achieve uniform filling of the voids and appropriate control of local stresses in nascent silicon structures (often having sub-micron dimensions). Excessive local stresses are detrimental because these stresses can lead to fractures, e.g., during the final release procedure, when sacrificial silicon oxide is removed and substantial stresses might occur.